Thin-film devices covered by the present invention include a circuit element such as an inductor, as well as a thin-film device using a magneto-resistive effect element (hereinafter referred to as “MR element”). Among them, the MR element is used not only as a magnetic detecting element or a magnetic memory but also as a reproducing element for a thin-film magnetic head. The inductor forms an independent circuit element by itself and is also used as a recording element for a thin-film magnetic head.
Typically, thin-film devices of this type tend to have a protective structure with a thin-film element embedded in an insulating film. This structure requires a lead conductor film for enabling electrical contact of the thin-film element inside the insulating film with the outside. Typically, the lead conductor film has a three-dimensional wiring structure composed of a planar portion and a projecting portion, wherein one end of the planar portion is connected to the thin-film element and at the other end, the projecting portion projects from the film surface of the planar portion in a film thickness direction of the insulating film. Moreover, the upper end of the projecting portion is led out to the surface of the insulating film, and a bump for external connection is formed on the led-out upper end face.
The projecting portion is formed as a plated film containing Cu as a main component because it is required to have a decreased electrical resistance and a relatively large thickness. Since the surface of the bump is intended to be connected to external wiring such as by bonding means, its outermost layer is formed by an Au plated film so as to meet the demand. For example, Japanese Unexamined Patent Application Publication No. H10-3614 can be cited as a prior art document in which the above bump structure is applied to a thin-film magnetic head.
In order to reliably perform wire bonding on the bump, however, the Au plated film to which the wire is to be bonded must have an excellent surface property. This is because poor surface property of the Au plated film lead to a problem of decrease in bonding strength or the like. Particularly in a thin-film device that requires a mechanical polishing process, typically a thin-film magnetic head, a polishing powder generated by slider processing or the like tends to be captured by unevenness on the surface of the Au plated film, interfering with bonding.
In a conventional bump structure in which the projecting portion of the lead conductor film is formed by a Cu plated film and an Au plated film is grown thereon using a Ti film as a seed film, however, the Au plated film grows to inherit the crystal structure of the Cu plated film (or epitaxially grows), which results in that the surface of the Au plated film becomes an uneven surface reflecting the crystal size and shape of the Cu plated film. This limits the improvement in surface property of the bump.